Esters from CLA (reaction product of conjugated linoleic acid and an alcohol) are known from eg WO 97/18320 or WO 99/32105. However the esters disclosed in WO 97/18320 are mainly the octylesters and these esters have the disadvantage that the alcohol residue is not food allowable and that therefore the use of these esters in foods is a problem. In this same document also glycerol esters of CLA isomers are disclosed which can be made from glycerol and free CLA by esterification. However during this esterification the enrichment in a specific CLA isomer (in general c9t11 or t10c12 CLA) is low or the reaction rate and/or yield for this conversion is very low. Moreover the products so obtained often are not very active for their desired health effect. Another problem is that the esters disclosed in WO ""105 often are derived from an alcohol that, although being food allowable is not readily available or is difficult to remove from the reaction mixture (eg tocopherol alcohol or ascorbyl alcohols or retinyl alcohols).
We studied whether we could find a solution for above problems. This study resulted in the finding of new esters of CLA isomers that can be made easily in good yields in relatively short times while the products obtained often displayed high enrichment rates in specific CLA-isomers (in particular in c9t11 and/or t10c12 isomers). Moreover the alcohols used herefore are food allowable and easily available and can be separated easily from the crude reaction mix resulting from the partial conversion of the free CLA with the alcohol.
Moreover we found that these esters displayed good health properties and excellent taste properties. In particular the taste of the esters was improved compared to the taste of the free acids.
Therefore our invention concerns in the first instance with esters of conjugated linoleic acid (xe2x88x92 CLA) and a food allowable alcohol wherein the food allowable alcohol is selected from terpene alcohols or sesquiterpene alcohols. In particular the use of the alcohols with general formula I, wherein 
R1=H, or forms together with R4 a Cxe2x80x94C bond,
R2=H or CH3
R3=H, CH3 or OH
R4=H or forms together with R1, or with R6 or with R14 a Cxe2x80x94C bond, or forms together with R9 a xe2x80x94Cxe2x80x94 bridge or forms together with R9 a
xe2x80x94Cxe2x80x94Cxe2x80x94Cxe2x80x94Cxe2x80x94 residue
II
(CH3)2 Cxe2x80x94C
R5=H or forms together with R13 or with R14 a Cxe2x80x94C bond
R6=H or forms together with R4 a Cxe2x80x94C bond
R7=H, or OH
R8=H or OH or forms together with R10 a Cxe2x80x94C bond
R9=H, or forms together with R4 a xe2x80x94Cxe2x80x94 bridge or a
xe2x80x94Cxe2x80x94Cxe2x80x94Cxe2x80x94Cxe2x80x94 residue
II
(CH3)2Cxe2x80x94C
R10=H or forms together with R8 or with R12 a Cxe2x80x94C bond
R11=H, i-propyl, i-propenyl, CH3 or forms together with R4 a xe2x80x94C(CH3)2-bridge
R12=H or forms together with R10 a Cxe2x80x94C bond
R13=H, OH, orxe2x80x94C(CH3)xe2x95x90Cxe2x80x94C(OH)xe2x80x94 or forms together with R5 a Cxe2x80x94C bond
R14=H, or forms together with R4 or R5 a Cxe2x80x94C bond lead to excellent results
In particular the invention is concerned with esters derived from an alcohol selected from the group consisting of menthol, isopulegol, methenol, carveol, carvomenthenol, carvomenthol, isobornylalcohol, caryophyllenealcohol, geraniol, farnesol and citronellol. These alcohols are all food allowed, easily available and give high enrichment in specific CLA isomers when converted partially with free CLA (in particular with a 50:50 mix of c9t11 and t10c12 CLA) along an enzymic route. Moreover the esters display good activity with respect to anti inflammatory and anti diabetic or insulin resistance effects and taste far better than the free CLA where they are derived from. The esters can be obtained easily in a form wherein the esters comprise more than 80 wt %, preferably more than 90 wt % and in particular more than 95 wt % of c9t11 plus t10c12 CLA isomers. Depending on the conversion that is applied the esters can be obtained as a mix wherein the c9t11 and t10c12 CLA-isomers are present in a weight ratio of 50:50, or as a mix wherein the c9t11:t10c12 isomers are present in a weight ratio of more than 70:30, in particular more than 80:20. The esters of the enriched isomer mix have the advantage that the mix mainly will display the specific health effects from the specific isomer present in high contents while the other specific health effects of the other isomer hardly will be noticed. This enables us to dose more specifically to achieve a specific health effect, while also the dosage of the CLA compound can be less which is of particular advantage if the esters are applied as food supplement because this will limit the size of the capsules and the smaller the capsules can be, the easier they can be swallowed by the consumer.
A particular preference exists for esters of CLA and menthol wherein more than 80 wt %, preferably more than 90 wt % of the CLA residue of the esters consists of c9t11-CLA, while less than 2 wt % of the total CLA-residue consists of CLA-isomers other than c9t11 and t10c12 and the esters contain less than 5 wt % preferably less than 3 wt % of free fatty acids. Administering of these products means that potentially negative side effects of other components can be avoided.
Our invention further concerns a process for the preparation of esters of conjugated linoleic acid (CLA) and a food allowable alcohol as defined above, wherein free conjugated linoleic acid is reacted with the food allowable alcohol in the presence of less than 1.8 wt % water and a lipase. This process will result in esters that can be used in food products as both components of the products are food allowable.
In the instance that an ester is desired wherein higher contents of a specific CLA-isomer is present the above process can be adapted to a process wherein a food allowable alcohol with the formula as defined above is reacted with a mix of free CLA with about 50% of both main isomers (c9t11 and t10c12) and wherein the reaction is performed by partially converting this mixture of c9t11 and t10c12 CLA in the presence of an enzyme than can discriminate between c9t11 and t10c12-CLA isomers and which enzyme preferably is Candida rugosa lipase, whereupon CLA-esters are isolated enriched in c9t11 CLA-isomer and free fatty esters are isolated as unconverted reactant enriched in t10c12 CLA isomer.
Other enzymes that can be applied are lipase D; lipase QL; lipase-SL; Mucor miehei lipase, optionally on a support such as duolite; Cand antartica lipase and lipozyme.
The different products can be obtained by working up the crude reaction product as follows:
first add a diluted base to the crude reaction mixture
then separate the water phase and the organic phase
followed by washing of the organic phase and adjusting the pH of this phase to pH 5-7
and finally by removal of the water from this phase, preferably by distillation.
By this route esters are obtained enriched in the c9t11 CLA isomer.
To obtain a free CLA product enriched in the t10c12 isomer the procedure is as follows:
the water phase of the reaction product obtained according to above process is acidified to a pH less than 3.0, preferably  less than 1.5,
whereupon the mixture obtained is separated in an upper layer and a residue and
the upper layer is washed with water and the water is removed therefrom.
According to another aspect of our invention our invention also concerns food products comprising a fat and a good tasting health component wherein the taste and health component is an ester according to the invention. The food products are specifically selected from the group consisting of spreads (10-90% fat contents); dressings, mayonnaise, cheese, ice cream, ice cream coatings; confectionery coatings or fillings; sauces and culinary products. These food products suitably contain 0.5 to 20 wt % of our novel CLA esters.
Our novel esters can also be used for the preparation of triglycerides containing CLA residues. Therefore an ester composition according to the invention can be converted with glycerol or with a vegetable oil in the presence of a base or an enzyme while in the instance that glycerol is converted the liberated alcohol residue from the esters of the CLA-esters is removed from the reaction mix during the conversion. This removal of liberated alcohol can be done by vacuum distillation or by molecular distillation.
According to a last embodiment our invention also concerns the use of our CLA esters as a good tasting health agent, in particular having anti-inflammatory or anti-diabetic or insulin resistant properties.